Abstract

Farm, cattle group and individual bovine risk factors for bovine tuberculosis (bTB) in cattle herds in the South West of England were explored.
A cohort study using 148 well characterised cattle herds was conducted in SW England 2001-2004. The study was set up in areas affected by foot-and-mouth disease in 2001 and all farms were taking part in the Randomised Badger Culling Trial (RBCT). The use of a standard questionnaire and national data records from the skin intradermal cervical comparative tuberculin test (SICCT) and from the British Cattle Movement Service (BCMS) databases were combined.
The two main statistical techniques used were survival analysis and multilevel logistic regression with random effects. Associations with the risk of herd breakdown with bTB were explored using survival analysis. The main factors associated with disclosure of reactor cattle were the purchase of cattle from markets and the storage of slurry and manure in close containment.
In the investigation of the risk of an individual bovine animal becoming a reactor using multilevel logistic regression with random effects analysis, explanatory variables at herd, individual cattle and test levels, were explored. The potential exposure to reactor cattle in previous tests was the most significant finding as a risk for a bovine animal reacting at a current test. Only 9/19,027 cattle became reactors if they had not been exposed to a reactor animal previously.
When the risk of an animal group having at least one reactor disclosed in the group was investigated using the location of the animal groups within the farm by monthly periods, the risk increased with the number of cattle in the groups when these were housed and with the presence of badgers in the fields when they were grazing.
This thesis has provided a deep investigation into the risk factors that can affect the introduction and persistence of infection with M. bovis in cattle herds, and the importance that cattle play in these factors has been highlighted.